40° phase-shifting autotransformer

Abstract

The invention relates to an autotransformer for transforming a three-phase power supply into a nine-phase power supply, notably for use in a rectifier. The autotransformer is a, step-up or step-down transformer. For a step-down application, the three-phase input terminals E1, E2, E3. are connected to one of the three main windings in delta configuration, mounted on respective magnetic branches M12, M23, M31 of a magnetic circuit. Te main winding B12 of one branch has intermediate taps K1, K'1, K''1 from which auxiliary windings X31, Y23, Z31, mounted on the other branches, start. These auxiliary windings produce, on three output terminals A1, B1, C1, voltages one of which is in phase with the three-phase supply voltage at E1, the other phase-shifted by +40°, and the third by +80°. The number of turns in the auxiliary windings and the position of the intermediate taps are calculated so as to obtain this result. The identical windings of the other branches produce the other output voltages on the terminals A2, B2, C2, A3, B3 in order to produce a system with nine phases.

The invention claimed is: 
     
       1. A step-up or step-down autotransformer, designed to be connected to a supply of three-phase voltage of given amplitude and supplying nine output voltages with phases separated in steps of 40° and of identical amplitudes, higher or lower than the amplitude between neutral and phase of the three-phase supply, the autotransformer comprising:
 a magnetic core with three branches and on each magnetic branch a main winding having a first and second terminal three main windings being electrically connected together in delta configuration, wherein the autotransformer also comprises, on each magnetic branch, three auxiliary windings, the main winding of a given branch having between its first and its second terminal, a first, a second and a third intermediate tap, the first auxiliary winding of another branch having a first terminal connected, respectively, to a first intermediate tap of the main winding of the given branch and a second input or output terminal having a voltage in phase with the voltage present on the first terminal of this main winding, the second and third auxiliary windings of the given branch each having a first terminal connected to a second or a third intermediate tap of one or the other of the other branches and a second terminal forming a respective output among nine outputs of the autotransformer. 
 
     
     
       2. The autotransformer as claimed in  claim 1 , wherein the first auxiliary winding of the first branch is connected to the first intermediate tap of the main winding of a second branch, the first terminal of the main winding of the second branch being connected to the second terminal of the main winding of the first branch. 
     
     
       3. The autotransformer as claimed in  claim 1 , wherein it forms a step-down autotransformer, the first and second terminals of the main windings being inputs of the autotransformer, designed to be supplied by the three-phase voltage to be transformed, and the second terminal of the first auxiliary winding of one branch forming a direct output of the autotransformer, in phase with a voltage on one terminal of the three-phase supply. 
     
     
       4. The autotransformer as claimed in  claim 2 , wherein it forms a step-down autotransformer, the first and second terminals of the main windings being inputs of the autotransformer, designed to be supplied by the three-phase voltage to be transformed, and the second terminal of the first auxiliary winding of one branch forming a direct output of the autotransformer, in phase with a voltage on one terminal of the three-phase supply. 
     
     
       5. The autotransformer as claimed in  claim 3 , wherein two main windings mounted on two different magnetic branches are connected to one input of the autotransformer, the auxiliary winding which is connected to the direct output in phase with the three-phase voltage present at this input being mounted on the third magnetic branch. 
     
     
       6. The autotransformer as claimed in  claim 4 , wherein two main windings mounted on two different magnetic branches are connected to one input of the autotransformer, the auxiliary winding which is connected to the direct output in phase with the three-phase voltage present at this input being mounted on the third magnetic branch. 
     
     
       7. The autotransformer as claimed in  claim 1 , wherein it forms a step-up autotransformer, the first and second terminals of the main windings being direct outputs of the autotransformer, in phase with the voltages of the three-phase supply, and the second terminal of the first auxiliary winding of each branch forming a respective input of the three-phase supply. 
     
     
       8. The autotransformer as claimed in  claim 2 , wherein it forms a step-up autotransformer, the first and second terminals of the main windings being direct outputs of the autotransformer, in phase with the voltages of the three-phase supply, and the second terminal of the first auxiliary winding of each branch forming a respective input of the three-phase supply. 
     
     
       9. The autotransformer as claimed in  claim 7 , wherein, two main windings, mounted on two different magnetic branches, being connected to the same direct output of the autotransformer in the delta configuration, the auxiliary winding connected to one input n phase with this output is mounted on the third magnetic branch. 
     
     
       10. The autotransformer as claimed in  claim 8 , wherein, two main windings, mounted on two different magnetic branches, being connected to the same direct output of the autotransformer in the delta configuration, the auxiliary winding connected to one input n phase with this output is mounted on the third magnetic branch. 
     
     
       11. The autotransformer as claimed in  claim 1 , wherein the first intermediate tap of a main winding is situated between a first terminal of this main winding and the second intermediate tap. 
     
     
       12. The autotransformer as claimed in  claim 1 , wherein the first intermediate tap of a main winding is situated between the second and third intermediate taps of this winding. 
     
     
       13. The autotransformer as claimed in  claim 1 , wherein, if two main windings connected to the same common terminal and the first intermediate tap provided on one of said two main windings are considered, a fourth intermediate tap is also provided situated on the other of said two main windings, with the same number of turns, on the one hand, between the common terminal and said first intermediate tap and, on the other hand, between the common terminal and said fourth intermediate tap, and, starting from these two intermediate taps, two auxiliary windings connected to said second input or output terminal which is in phase with the voltage on the common terminal. 
     
     
       14. An AC/DC converter comprising an autotransformer as claimed in  claim 1 , a forward-biased diode being connected between each output of the autotransformer and a positive output of the converter and a reverse-biased diode being connected between each output of the autotransformer and a negative output of the converter. 
     
     
       15. An AC/DC converter comprising an autotransformer as claimed in  claim 2 , a forward-biased diode being connected between each output of the autotransformer and a positive output of the converter and a reverse-biased diode being connected between each output of the autotransformer and a negative output of the converter. 
     
     
       16. An AC/DC converter comprising an autotransformer as claimed in  claim 3 , a forward-biased diode being connected between each output of the autotransformer and a positive output of the converter and a reverse-biased diode being connected between each output of the autotransformer and a negative output of the converter. 
     
     
       17. An AC/DC converter comprising an autotransformer as claimed in  claim 7 , a forward-biased diode being connected between each output of the autotransformer and a positive output of the converter and a reverse-biased diode being connected between each output of the autotransformer and a negative output of the converter. 
     
     
       18. An AC/DC converter comprising an autotransformer as claimed in  claim 2 , a forward-biased diode being connected between each output of the autotransformer and a positive output of the converter and a reverse-biased diode being connected between each output of the autotransformer and a negative output of the converter. 
     
     
       19. An AC/DC converter comprising an autotransformer as claimed in  claim 12 , a forward-biased diode being connected between each output of the autotransformer and a positive output of the converter and a reverse-biased diode being connected between each output of the autotransformer and a negative output of the converter. 
     
     
       20. An AC/DC converter comprising an autotransformer as claimed in  claim 13 , a forward-biased diode being connected between each output of the autotransformer and a positive output of the converter and a reverse-biased diode being connected between each output of the autotransformer and a negative output of the converter.